Sealing apparatus for transport of material between regions at different pressures

ABSTRACT

A seal to permit the passage of material, such as a continuous web bearing a layer of coating composition, between two zones at different gas pressures comprises a narrow passageway in communication with the two zones, a plurality of transverse ribs spaced along the longitudinal extent of the passageway, and a plurality of spaced apertures located within the troughs between adjacent ribs and communicating with a vacuum manifold for withdrawing gas from the passageway to provide a progressive change in pressure from a value at the inlet to the passageway equivalent to the pressure in the zone from which material is being transported to a value at the outlet from the passageway equivalent to the pressure in the zone into which the material is being transported. In a preferred embodiment, the seal is comprised of a smooth arcuate plate and a curved castellated shoe positioned opposite and in close proximity to the plate to define a narrow arcuate passageway therebetween. The seal is especially useful in the vacuum drying of web material having a surface coating which is especially susceptible to damage, such as a web consisting of a support coated with one or more layers of photographic emulsion.

United States Patent Saunders amas Mar, M, 1972 PrimaryExaminerFrederick L. Matteson Assistant Examiner-Harry B. RameyAttorney-Walter O. Hodsdon and Alfred P. Lorenzo [5 7 ABSTRACT A seal topermit the passage of material, such as a continuous web bearing a layerof coating composition, between two zones at different gas pressurescomprises a narrow passageway in communication with the two zones, aplurality of transverse ribs spaced along the longitudinal extent of thepassageway, and a plurality of spaced apertures located within thetroughs between adjacent ribs and communicating with a vacuum manifoldfor withdrawing gas from the passageway to provide a progressive changein pressure from a value at the inlet to the passageway equivalent tothe pressure in the zone from which material is being transported to avalue at the outlet from the passageway equivalent to the pressure inthe zone into which the material is being transported. in a preferredembodiment, the seal is comprised of a smooth arcuate plate and a curvedcastellated shoe positioned opposite and in close proximity to the plateto define a narrow arcuate passageway therebetween. The seal isespecially useful in the vacuum drying of web material having a surfacecoating which is especially susceptible to damage, such as a webconsisting of a support coated with one or more layers of'photographicemulsion.

7 Claims, 3 Drawing Figures PMENTEDMAR 14 I972 SHEET 1 0F 2 R0 GER LvSAUNDERS INVENTOR.

PATENTEDHAR 14 I972 3, 6A8 883 SHEET 2 OF 2 ROGER L. SAUNDERS INVENTOR.

SEALING APPARATUS FOR TRANSPORT OF MATERIAL BETWEEN REGIONS AT DIFFERENTPRESSURES The present invention relates to seals for use between twozones at different pressures when transporting material between the twozones and to methods of providing such seals.

The seal of the present invention has the advantage that is ofparticular utility where it is desired to transport a material having areadily damageable coating between two zones at different gas pressureswithout damage to the coating and without substantial passage of gasbetween the two zones.

According to the present invention, there is provided a seal for usebetween two zones at different pressures when transporting materialbetween the two zones, the seal comprising means defining a narrowpassageway in communication with each of the two zones through which, inuse, a material is transportable and means for progressively changingthe gas pressure through the length of the passageway, when the seal isin use, from a value, at the inlet to the passageway, equivalent to thepressure in the zone from which the material is being transported to avalue, at the outlet from the passageway, equivalent to the pressure inthe zone into which the material is being transported.

In a preferred embodiment of the invention, the narrow passageway isdefined by a surface, arranged to carry the material to be transported,and a shoe positioned opposite the surface; the show having a pluralityof apertures extending therethrough which are connected to a means fortransferring gas into or out of the passageway. Preferably, the shoecomprises a series of surface irregularities extending transversely ofthe passageway, respective apertures being located in troughs of thesurface irregularities. The apertures and surface irregularities enablethe pressure in the passageway to be changed progressively along itslength. Conveniently, the surface arranged to carry the material is apolished plate formed of, for example stainless steel. The plate may betreated to reduce friction, for example, with polytetrafluoroethylenewhich may be applied in the form of an aerosol spray. Additionally, theplate may be cooled, for example, by the circulation of water at arelatively low temperature. In an alternative embodiment of theinvention, the surface may be defined by a roller mounted for rotationin the direction in which the material is being transported.

Preferably, the seal also comprises means for preventing inflow of gasthrough the sides of the narrow passageway. For example, where thesurface is a polished plate, gaskets, which may be made of rubber, canbe provided along the sides of the passageway.

Advantageously, the surface irregularities of the shoe are in the formof castellations comprising upstanding ribs having the troughstherebetween. Preferably, each rib has a plurality of grooves extendinglongitudinally thereof.

The seal of the present invention is particularly useful where it isdesired to transport a material from a zone at a first pressure toanother zone at a second, lesser pressure. In this case, the means fortransferring gas is in the form of one or more manifolds connected to avacuum pump or respective pumps.

The narrow passageway should be of dimensions greater, but notsubstantially greater, than the material to be transported. For example,the point of closest approach of the shoe and the material to betransported may be of the order of 0.010 to 0.013 inch, although smalleror larger gaps may be used.

The seal of the present invention is particularly useful where thematerial is in the form of a web. In this case, the narrow passageway ispreferably arcuate longitudinally so that the web may be maintainedunder slight tension. As described more fully hereinafter, the webmaterial may be a photographic material comprising a support havingcoated thereon one or more hydrophilic colloid layers e.g., lightsensitive silver halide emulsion layers. Other applications include thetransfer of webs coated with liquids having high viscosity, ofadhesively coated webs, and of webs coated with set, nonhydrophiliccolloids.

According to the present invention, there is further provided anapparatus comprising a chamber defining a zone arranged to be maintainedat a pressure different from ambient pressure, said chamber having aninlet and an outlet through each of which a material is transportable,and wherein at least the inlet is provided with a sea] as aforestated.

Preferably, the apparatus is a vacuum drying apparatus and the chamberis a low-pressure enclosure.

According to the present invention, there is also provided a method oftransporting a material between two zones maintained at differentpressures, wherein the fluid pressure acting on the material isprogressively changed from a value equivalent to that of the zone fromwhich the material is being transported to a value equivalent to that ofthe zone into which the material is being transported.

In a preferred embodiment of the invention, the material is transferredfrom a zone at a particular pressure, e.g., ambient atmosphericpressure, to a zone maintained at a lower pressure. This embodiment ofthe invention is particularly useful where it is desired to dry coatedhydrophilic colloid layers, e.g., light sensitive silver halide emulsionlayers. The hydrophilic colloid layers may have been previously chilled.

The invention will now be described further with reference to theaccompanying drawings, in which:

FIG. 1 is a partial, schematic view of a seal according to the presentinvention taken along the line l-l of FIG. 3;

FIG. 2 is a schematic view of a vacuum drying apparatus incorporating aseal according to the present invention; and

FIG. 3 is a fragmentary view, to an enlarged scale, of part of the sealshown in FIG. 1.

In FIG. 1 there is shown a seal 10 which is mounted on a vacuum chamberllll by means of a backing plate 12. The seal 10 comprises a polishedarcuate surface 13, formed, for example, of a stainless steel. Thesurface 13 is attached to the backing plate 12 by means of bolts (notshown). The surface 13 is treated to reduce friction e.g., bypolytetrafluoroethylene applied in the form of an aerosol spray, and isprovided with a cooling means (not shown) e.g., means for circulatingrelatively low temperature water. A web M, for example, a coatedphotographic material, is arranged to be passed over the surface 13through an inlet 15 into the vacuum chamber II in the directionindicated by the arrow 16.

The seal 10 further comprises a shoe 17 of substantially the samearcuate shape as the surface 13 and] mounted closely adjacent thereto todefine a narrow passageway 18. The show 17 comprises a series oftransverse castellations comprising upstanding ribs 19 (some of whichare not shown) interspersed by troughs 20. The point of closest approachof the ribs and the web is preferably constant and of the order of 0.010to 0.013 inch but smaller or larger gaps may be used.

Preferably, means are provided for sealing the narrow passageway 18along the sides thereof to prevent inflow of air therethrough. Forexample, gaskets (not shown), which may be made of rubber, can beprovided along each side of the narrow passageway 18. Within each of thetroughs 20 a plurality of apertures 21 are provided (See FIG. 3). In apreferred em bodiment, the ribs 19 have a plurality of lengthwisegrooves 25 therealong. The apertures 21 extend radially of the arcuateshape of and through the shoe 17. A plurality of manifolds 24 (only oneof which is shown) which each communicate with respective troughs 20 aremounted externally of the shoe l7 and are connected to a vacuum pump(not shown). In the embodiment illustrated, the arcuate shape of thepassageway 18 enables the web M to be maintained under slight tension.

In FIG. 2 there is shown a vacuum drying apparatus 22 comprising avacuum chamber 11 upon which is mounted a backing plate 12. The vacuumchamber 11 comprises an inlet and an outlet 23. Mounted externally ofthe chamber 1 1 at the inlet 15 is a seal 10 of the type shown inFIG. 1. Mounted externally of the chamber 11 at the outlet 23 is afurther seal (not shown) which may be in accordance with the presentinvention or may be a conventional seal, such as contacting rollershaving wipers, as the coated material is by such time dry. Heating means26 are provided in the chamber 11.

In FIG. 3 there is shown a part of the shoe 17, to an enlarged scale,wherein the construction of the ribs 19, troughs 20, apertures 21 andalso the lengthwise grooves 25 can be seen more clearly.

In operation, a material such as a web 14 in the form of a chilled,undried photographic material coated with hydrophilic colloid layers istransported through the seal 10 and into the vacuum chamber 11.

The vacuum pump is energized and draws air through the apertures 21 fromthe narrow passageway 18 defined by the surface 13 and the shoe 17.Thus, the pressure within the narrow passageway 18 is reducedprogressively in the direction of travel of the material from theexternal pressure at the inlet to the seal, to a value, at the exit fromthe seal, which is preferably equivalent to the pressure inside thevacuum chamber 11. This is because the air travelling with the materialthrough the seal 10 has to pass successively through a plurality ofshort, narrow passages defined between the ribs 19 and the surface 13with wider passages defined by the troughs 20 and the surface 13therebetween. The pressure profile within the seal 10 may be measured bypressure tappings and suitable pressure gauges or manometers. It may benecessary to control this pressure profile by adjusting the pumpingspeed of the vacuum pump or by altering the number of apertures 21 inparticular troughs 20, through which air can be drawn, in order to avoidpossible damage to the coating of the material. Alternatively, valvemeans (not shown) may be located between each manifold 24 and the pumpto regulate the rate at which air is drawn through the respectivemanifolds. In the embodiment shown, the web 14 is coated on one sideonly and the coated side faces the shoe 17.

In an alternative embodiment of the invention, the surface 13 may bedefined by a roller mounted for rotation in the direction in which thematerial is being transported. In this case, a further seal would beprovided in the chamber 11 at the exit of the surface and at the sidesof the roller.

A number of other parameters have to be taken into account whenoperating the seal in drying a photographic material, to avoid damage tocoating of the material being transported. These are:

a. the seal length and the number and size of the castellations; b. gapthickness between the seal and the coating;

c. pressure difference between the inlet and exit of the seal;

(1. temperature of the arcuate surface;

e. the type of hydrophilic colloid used and concentration thereof;

f. the presence or absence of salts modifying the character of thecolloid; and

g. treatment of the coated web, particularly, chilling thereof betweenthe point at which it is coated and that at which it enters the seal.

The properties of the seal were investigated using a coating and settingunit. A -inch wide web moving at a speed of 5 feet per minute was coatedwith gelatin solution and chilled by contact with a water cooled metalplate for seconds. The set web was then exposed to room air for secondsand then passed into one or other of the two seals (a) and (b) describedbelow. After passing through the seal into a low-pressure enclosure, theweb was visually examined through a window. The seal and enclosure areshown in FIG. 2.

One or other of two seals (a) and (b) substantially as shown in FIG. 1were used. The seals had the following dimensions:

Length of film path in seal 5" 15" Width ofseal 6" 6" Width of web 5" 5"No. of ribs I6 60 No. of manifolds 4 12 Length in direction of seal ofribs Va" 9/64" Length in direction of seal of troughs W 7/64" No. ofholes per trough l0 14 Size of holes M" 7/64" N0, oftroughs per vacuumconnection 3 5 Height of ribs l6" k" EXAMPLE 1 Seal (a) Coatingsolution-5 percent gelatin containing black colloidal silver pigmentCoating thickness0.002 inch Pressure in vacuum chamber-230 mm. Hg

Table I gives the pressure at each trough in the seal.

EXAMPLE 2 Seal (a) Coating solution-5 percent gelatin containing a blackcolloidal silver pigment Coating thickness0.004 inch Pressure in vacuumchamber 570 mm. Hg

Table I gives the pressure at each trough in the seal.

EXAMPLE 3 Seal (a) Coating solution7 percent gelatin containing a blackcolloidal silver pigment Coating thickness 0.002 inch I Pressure invacuum chamber-230 mm. Hg

Table I gives the pressure at each trough in the seal.

EXAMPLE 4 Seal (a) Coating solution7 percent gelatin containing a blackcolloidal silver pigment Coating thickness-0.004 inch Pressure in vacuumchamber-380 mm. Hg

Table I gives the pressure at each trough in the seal.

EXAMPLE 5 Seal (b) Coating solution-4 percent gelatin solutioncontaining colloidal silver pigment Coating thickness0.002 inch Pressurein vacuum chamber-8.4 mm. Hg

Table II gives the pressure at each trough in the seal.

EXAMPLE 6 Seal (b) Coating solutionS percent gelatin solution containingcolloidal silver pigment Coating thickness-0.004 inch pressure in vacuumchamber-J3 mm. Hg

Table II gives the pressure at each trough in the seal.

EXAMPLE 7 Seal (b) Coating solution7 percent gelatin solution containingcolloidal silver pigment Coating thickness0.004 inch Pressure in vacuumchamber-7.0 mm. Hg

Table II gives the pressure at each trough in the seal.

An unsuitable pressure profile within the seal will produce damage to acoated web because of excessive air movement within the seal.

By adopting nonoptimum pressure profiles, damage was caused to thecoating. However, if under these circumstances the chilling and settingof the web was improved, the damage to the coating could be lessened orobviated. Hence, the limits obtained (i.e., of colloid concentration andcoating thickness) are peculiar to the equipment used, and in no wayrepresent the limits of the invention. Modifications to the seal orchill section should make it possible to convey weaker and thickercoatings.

TABLE 1 Pressures (mm. Hg) at various points along seal (a) for Examples1 to 4 Example l 2 3 4 Colloid concentration 5% 5% 7% 7% Coatingthickness 0.002" 0.004" 0.002" 0.004" Atmospheric pressure 760 760 760760 Pressure at trough 2 665 760 740 730 Pressure at trough 3 630 760730 710 Pressure at trough 4 605 760 726 695 Pressure at trough 6 750636 650 Pressure at trough 7 400 745 600 630 Pressure at trough 8 400740 580 615 Pressure at trough 9 420 735 570 580 Pressure at trough 10340 730 530 550 Pressure at trough 11 290 720 500 500 Pressure at trough13 300 690 460 500 Pressure at trough 14 290 670 395 470 Pressure attrough 265 640 290 430 Pressure in vacuum chamber 230 570 230 380 TABLE11 Pressures (mm. Hg) at various points along seal (b) for Examples 5 to7 Example 5 6 7 Colloid concentration 4% 5% 7% Coating thickness 0.002"0.004" 0.004" Atmospheric pressure 757 747 753 Pressure at trough No. 6686 694 Pressure at trough No. 7 674 684 Pressure at trough No. 8 658674 648 Pressure at trough No.9 646 667 631 Pressure at trough No. 10636 659 621 Pressure at trough No. 11 628 652 607 Pressure at trough No.12 619 644 605 Pressure at trough No. 13 606 634 576 Pressure at troughNo 14 590 624 559 Pressure at trough No. 15 576 614 539 Pressure attrough No. 16 559 600 517 Pressure at trough No. 17 545 588 494 Pressureat trough No. 18. 516 565 464 Pressure at trough No. 19 493 538 427Pressure at trough No. 20 469 525 469 Pressure at trough No. 21 424 496332 Pressure at trough No. 22 40] 487 295 Pressure at trough No.23 341443 246 Pressure at trough Nov 24 295 419 250 Pressure at trough No. 25279 412 240 Pressure at trough No, 26 270 354 199 Pressure at troughNo.27 242 311 164 Pressure at trough No. 2B 219 288 150 Pressure attrough No.29 191 233 149 Pressure at trough No. 30 190 230 141 Pressureat trough No.31 H36 225 131 Pressure at trough No, 32 174 210 103Pressure at trough No.33 I56 183 87 Pressure at trough No, 34 134 150 85Pressure at trough No. 35 131 146 79 Pressure at trough No. 36 116 13067 Pressure at trough No.37 93 101 54 Pressure at trough No. 3B 84 88Pressure at trough No. 39 80 87 Pressure ut trough No.40 78 84 Pressureat trough No. 41 68 70 36 Pressure ut trough No. 42 60 60 31 Pressure attrough No. 43 54 54 27 Pressure at trough No. 44 51 52 26 Pressure attrough No. 45 50 50 25 Pressure at trough Nov 46 44 44 21 Pressure attrough No. 47 3B 40 18 Pressure at trough No. 48 37 35 16 Pressure attrough No. 49 36 33 16 Pressure at trough No. 50 36 34 15 Pressure attrough No. 51 33 31 14 Pressure at trough No. 52 30 29 14 Pressure attrough NO. 53 26 26 14 Pressure at trough No. 54 25 23 11 Pressure attrough No. 55 25 24 14 Pressure at trough No. 56 24 23 14 Pressure attrough No. 57 22 21 14 Pressure at trough No, 58 l7 l7 13 Pressure attrough No. 59 I6 16 13 Pressure at trough No. 60 l4 l3 12 Pressure invacuum chamber 84 7.3 7.0

It will be appreciated that webs wider than 5 inches can be transportedthrough a seal according to the invention providing the mechanicalstrength of the seal is adequate to withstand the pressures involved.

If desired, the spacing between the coated layer and the seal can bevaried beyond the limits used in the examples. However, larger spacingsrequire more air removal capacity while smaller spacings require moreprecise control of web movement.

If it is desired to transport weaker colloid solutions, a shoe havingmore castellations and using a more gradual pressure profile may beused.

Modifications within the scope of the present invention are envisaged.For example, if a web coated on both sides was to be transported, adouble seal in which a castellated shoe was mounted on both sides of theinlet to the vacuum chamber could be used. It would be necessary,however, for the narrow passageway to have a planar shape. In this waythe coated web would make no physical contact with the seal.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

1 claim:

1. Sealing apparatus for the passage of material between two zones atdifferent gas pressures, comprising a continuous plate; a shoe mountedopposite said plate and narrowly spaced therefrom to form a continuousnarrow passageway therebetween having an open inlet and outlet incommunication with opposite ones of said zones for passage of saidmaterial between said zones, the surface of said shoe forming onesurface of said passageway including a plurality of trans verse ribswhich extend into said passageway and are spaced along the lengththereof, said shoe provided with a plurality of apertures incommunication with said passageway and located between adjacent ribs,and a vacuum manifold system in communication with said plurality ofapertures for maintaining a pressure within said passageway whichprogressively changes from a pressure at the inlet to said passagewayequivalent to the pressure in the zone from which the material enters toa pressure at the outlet of said passageway equivalent to the pressurein the Zone into which the material passes.

2. Apparatus as described in claim 1 wherein said plate is of an arcuateconfiguration and said shoe is curved to correspond to the configurationof said plate and thereby form an arcuate passageway.

3. Sealing apparatus for the passage of a continuous web between twozones at different gas pressures, comprising a smooth arcuate plate forslideably supporting said web,

a curved shoe mounted opposite said plate and narrowly spaced therefromto form an arcuate passageway therebetween for passage of said web, saidshoe having a plurality of transversely extending ribs spaced along itslongitudinal extent and protruding into said passageway and a pluralityof spaced apertures within each of the troughs between adjacent ribscommunicating with said passageway, and

a vacuum manifold system communicating with said plurality of aperturesfor withdrawing gas from said passageway through said apertures.

4. Sealing apparatus for sealing a port within a wall to permit thepassage of a continuous web therethrough while maintaining a differentgas pressure on each side of said wall, comprising an arcuate platemounted on said wall adjacent said port for slideably supporting saidweb and directing it through said port,

a curved shoe mounted opposite said plate and narrowly spaced therefromto form an arcuate passageway therebetween for passage of said web, saidshoe having a plurality of transversely extending ribs spaced along itslongitudinal extent and protruding into said passageway and a pluralityof spaced apertures within each of the troughs between adjacent ribscommunicating with said passageway,

a manifold communicating with said apertures, and

a vacuum pump operatively connected to said manifold for withdrawing gasfrom said passageway via said apertures.

5. Apparatus as described in claim 4 including a backing plate to whichsaid arcuate plate and said shoe are affixed for mounting on said wall.

6. Apparatus as described in claim 3 wherein the distance between saidarcuate plate and said curved shoe is such that the point of closestapproach of said web material to said ribs is from about 0.010 to about0.0l 3 inch.

7. Apparatus as described in claim 3 wherein each of said ribs isprovided with a plurality of longitudinally extending grooves in thesurface of the rib directly opposite to said arcuate plate.

1. Sealing apparatus for the passage of material between two zones atdifferent gas pressures, comprising a continuous plate; a shoe mountedopposite said plate and narrowly spaced therefrom to form a continuousnarrow passageway therebetween having an open inlet and outlet incommunication with opposite ones of said zones for passage of saidmaterial between said zones, the surface of said shoe forming onesurface of said passageway including a plurality of transverse ribswhich extend into said passageway and are spaced along the lengththereof, said shoe provided with a plurality of apertures incommunication with said passageway and located between adjacent ribs,and a vacuum manifold system in communication with said plurality ofapertures for maintaining a pressure within said passageway whichprogressively changes from a pressure at the inlet to said passagewayequivalent to the pressure in the zone from which the material enters toa pressure at the outlet of said passageway equivalent to the pressurein the zone into which the material passes.
 2. Apparatus as described inclaim 1 wherein said plate is of an arcuate configuration and said shoeis curved to correspond to the configuration of said plate and therebyform an arcuate passageway.
 3. Sealing apparatus for the passage of acontinuous web betwEen two zones at different gas pressures, comprisinga smooth arcuate plate for slideably supporting said web, a curved shoemounted opposite said plate and narrowly spaced therefrom to form anarcuate passageway therebetween for passage of said web, said shoehaving a plurality of transversely extending ribs spaced along itslongitudinal extent and protruding into said passageway and a pluralityof spaced apertures within each of the troughs between adjacent ribscommunicating with said passageway, and a vacuum manifold systemcommunicating with said plurality of apertures for withdrawing gas fromsaid passageway through said apertures.
 4. Sealing apparatus for sealinga port within a wall to permit the passage of a continuous webtherethrough while maintaining a different gas pressure on each side ofsaid wall, comprising an arcuate plate mounted on said wall adjacentsaid port for slideably supporting said web and directing it throughsaid port, a curved shoe mounted opposite said plate and narrowly spacedtherefrom to form an arcuate passageway therebetween for passage of saidweb, said shoe having a plurality of transversely extending ribs spacedalong its longitudinal extent and protruding into said passageway and aplurality of spaced apertures within each of the troughs betweenadjacent ribs communicating with said passageway, a manifoldcommunicating with said apertures, and a vacuum pump operativelyconnected to said manifold for withdrawing gas from said passageway viasaid apertures.
 5. Apparatus as described in claim 4 including a backingplate to which said arcuate plate and said shoe are affixed for mountingon said wall.
 6. Apparatus as described in claim 3 wherein the distancebetween said arcuate plate and said curved shoe is such that the pointof closest approach of said web material to said ribs is from about0.010 to about 0.013 inch.
 7. Apparatus as described in claim 3 whereineach of said ribs is provided with a plurality of longitudinallyextending grooves in the surface of the rib directly opposite to saidarcuate plate.